1. Field of the Invention
This invention relates generally to an image delivery and display system, and more particularly to a technique for retrieving tiled image data that may be used, for example, in connection with a client-server network, wherein a center tile of the requested image is transmitted and displayed on the client computer first followed by the surrounding tiles in spiral order.
2. Description of the Related Art
In a client-server network, the server is a relatively large computer which manages files and databases for smaller client computers and also controls the interconnecting networks. A client-server network may be used, for example, in connection with a navigation system wherein a stationary server computer stores a street map covering the entire United States and a client computer on-board a vehicle accesses some portion of that map by specifying certain x, y map coordinates.
Upon receiving the specified x, y coordinates from the client computer, the server (which typically stores the map image in compressed form) decompresses the map image, partitions the image into tiles, extracts the tile containing the x, y coordinates and a certain number of surrounding tiles, recompresses those tiles and transmits this map data to the client computer. Upon receiving the compressed map data, the client computer decompresses the data and displays the map on the screen. The problem is that the tiles are typically decompressed and displayed from left to right, top to bottom, as indicated by the arrows on the tiled map image 11 shown in FIG. 1. Since the tile containing the x, y coordinates is in or near the middle, some time elapses before the client computer actually displays the tile containing the x, y coordinates, which is the tile of most interest to the operator of the vehicle.
Various proposals have been made for capturing, storing, transmitting and/or displaying images in connection with on-board navigation or display systems and/or map generating systems. However, none of these proposals solve the aforementioned problem.
In U.S. Pat. Nos. 4,630,065 and 4,660,037, devices have been developed for visually indicating the current location of an automotive vehicle. A mechanism assesses the coordinates of the moving vehicle using its direction and distance traveled, and displays the vehicle coordinates along with a map of the region. In the first patent, a series of local maps of an extended area are stored on microfilm as a photographic image collection and are individually available for viewing on a display. In the second patent, the map image information of the extended area is stored in digital form such that a portion of the map may be accessed for viewing.
On-board navigation systems have also been proposed for use in connection with aircraft. One such system is set forth in U.S. Pat. No. 5,057,835. The map and text display system proposed therein offers several "functionality" features such as conditional display of text, runway orientations, etc. Another such system has been proposed in U.S. Pat. No. 4,405,943. This patent provides a low bandwidth video imaging and transmission system that is used with a remotely piloted vehicle. High resolution images are captured in real time using a camera on an aircraft and then transferred to a memory aboard the aircraft. To reduce bandwidth, only a selected portion of the image is retrieved from ground as high resolution data; the remaining portion is retrieved as low resolution data. Another digital map display system for an aircraft is set forth in U.S. Pat. No. 4,876,651. This system includes a mass memory unit and a cache memory with display and map data transfer occurring in parallel.
Another patent directed to an electronic global map generating system is U.S. Pat. No. 4,972,319. The system therein uses a hierarchical tiling scheme. Map data is organized into a hierarchy of successive magnitudes for storage and presentation of map images at various resolutions.
However, none of these patents teach or suggest a tiled-image delivery and display system with a spirally rendered presentation of the tiles beginning with a center tile.